The invention relates to precast concrete slabs having raised domes to alert the visually handicapped of hazardous conditions by being placed in walkways, roadways, platform edges and areas of pedestrian traffic. The Americans with Disabilities Act Accessibility Guidelines (ADAAG), promulgated by the Access Board, an independent U.S. federal agency, established standards for tactile, detectable warnings for the visually impaired at street crossings, curb ramps, median islands and rail lines. These surfaces feature a distinctive pattern of raised truncated domes that provide a tactile cue detectable by cane or underfoot at the boundary between pedestrian and vehicular routes. The guidelines specify use of truncated domes aligned in a square grid pattern. The ADAAG call for a base diameter of 0.9 inches (23 mm) to 1.4 inches (36 mm), a top diameter of 50% to 65% of the base diameter and a height of 0.2 inches (5 mm). The center-to-center dome spacing is set at 1.6 inches (41 mm) to 2.4 inches (61 mm), with a minimum base-to-base spacing of 0.65 inches (16 mm). The surfaces are required to extend 24 inches (610 mm) in the direction of pedestrian travel and the full width of the curb ramp, landing, or blended transition.
One approach to adding the truncated dome warning is to form them on tiles designed to be glued or fastened to existing concrete. Tiles installed according to this method are not flush with the walking surface and are prone to peeling up or coming detached from the surface under certain weather conditions which cause concrete to expand and contract. Another approach, which is quite labor-intensive, is to set precast tiles into a required location which is being poured. Precast tiles set in fresh concrete must be installed when the concrete is at a proper state; the tiles will float up if concrete is too wet and will not set properly when concrete has cured faster than expected. Production time is lost due to waiting for the proper conditions for installation.
Yet another approach is a method of stamping the surface of concrete when it has reached a plasticity state. This method produces inconsistent texture and imperfections that bring the surface “out of spec”. The installer has only a limited time to try to fix the surface before the concrete sets. Stamping also raises only the fines of the concrete, reducing the strength in the domes.
Known in the art is a method of placing brick pavers with domes raised on the surface. This method requires setting a block out in the concrete, increasing labor time and form materials. Also, brick pavers have numerous spaces between them.
Accordingly, what is needed is a system and method that allow the precast concrete slabs to be set in the ramp after the frame has been cast in place in the fresh concrete. Reducing the labor time while the fresh concrete is being poured and making it easy for the people in the field to set the frames and, after the ramp has cured, to set slabs, cuts down on labor cost.